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From:   "Wang, Haiyue" <haiyue.wang@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: RE: [PATCH v1] mm: migration: fix the FOLL_GET failure on following
 huge page
Thread-Topic: [PATCH v1] mm: migration: fix the FOLL_GET failure on following
 huge page
Thread-Index: AQHYrihn+urE8ucWPUyypvMRNXxw+q2tfIKAgABlxrA=
Date:   Sun, 14 Aug 2022 06:20:13 +0000
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 <20220813162837.cc20e208e7a9d65fd2e7dc14@linux-foundation.org>
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> -----Original Message-----
> From: Andrew Morton <akpm@linux-foundation.org>
> Sent: Sunday, August 14, 2022 07:29
> To: Wang, Haiyue <haiyue.wang@intel.com>
> Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; david@redhat.com; l=
inmiaohe@huawei.com; Huang,
> Ying <ying.huang@intel.com>; songmuchun@bytedance.com; naoya.horiguchi@li=
nux.dev
> Subject: Re: [PATCH v1] mm: migration: fix the FOLL_GET failure on follow=
ing huge page
>=20
> On Fri, 12 Aug 2022 16:49:21 +0800 Haiyue Wang <haiyue.wang@intel.com> wr=
ote:
>=20
> > Not all huge page APIs support FOLL_GET option, so the __NR_move_pages
> > will fail to get the page node information for huge page.
>=20
> Which ones need fixing?

1. 'follow_huge_pud' arch/s390/mm/hugetlbpage.c

2. 'follow_huge_addr' arch/ia64/mm/hugetlbpage.c

3. 'follow_huge_pgd' mm/hugetlb.c

And I found that only 'pud' and 'pmd' need to check 'is_vm_hugetlb_page' li=
ke:
pud_huge(*pud) && is_vm_hugetlb_page(vma)
pmd_huge(pmdval) && is_vm_hugetlb_page(vma)

So I'm not sure whether my patch can cover 2 & 3 for other huge page use ca=
ses
except by hugetlbfs.

>=20
> What are the user-visible runtime effects of this bug?
>=20

In my test, the '__NR_move_pages' system call will return '-2' for 1GB huge=
 page
memory map when dump the page node information. [Test on linux-5.19 stable]

> Is a -stable backport warranted?

Yes.

Since the mainline has introduced the new patch:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?=
id=3D3218f8712d6bb

The backported needs to rebase like for 5.19:

-		if (page && !is_zone_device_page(page)) {
+		if (page) {

>=20
> > This is an temporary solution to mitigate the racing fix.
> >
> > After supporting follow huge page by FOLL_GET is done, this fix can be
> > reverted safely.
> >